1. Field of the Invention
The present invention relates to a zoom lens system having a vibration reduction function. More particularly, the present invention relates to vibration reduction for zoom lenses used in photographing cameras and video cameras.
2. Description of Related Art
An example of a conventional zoom lens system having a vibration reduction function is disclosed in U.S. Pat. No. 5,270,857, the subject matter of which is incorporated herein by reference. In this zoom lens system, vibration reduction correction is performed by displacing the entire or part of the lens group that moves during zooming in a direction perpendicular to the optical axis.
"Vibration reduction" refers to a process of correcting variations of image positions caused by shaking of the hand through movement of the lens group in a direction substantially perpendicular to the optical axis. "Vibration Reduction" causes a result of "image stabilizing."
However, in the above-described conventional zoom lens system having the vibration reduction function, the lens group that moves in the direction perpendicular to the optical axis also moves along the optical axis during zooming. Hence, problems occur because of the complexity of the mechanism for driving the vibration reduction lens group. The F-number becomes large to about 3.5-5.6 while the back focal length for a single lens reflex camera cannot be achieved.